As is described further in the background discussion below, photosensor devices associated with auto-darkening lenses have been used in the past to detect welding. For example, a photosensor and an associated circuit (sometimes referred to as “control circuit,” “operating circuit,” “drive circuit,” etc.) respond to the bright light at the beginning of welding, e.g., when a person ignites a welding torch, e.g., flame type, electric arc type, etc., to carry out a welding process. Upon detecting the bright light that occurs at the start of welding, the photosensor and associated circuit cause the shutter of an auto-darkening welding lens to go automatically to a dark state, whereby light transmission through the welding lens is reduced and the eyes of the person carrying out the welding process are protected from the bright light. When the bright light ceases, which would indicate cessation of welding, the photosensor and associated circuit cause the auto-darkening lens to increase light transmission to a relatively clear or bright state.
Reference herein to light may be visible light, ultraviolet light, infrared light, or other types of electromagnetic energy that would affect the eyes of a person, such that the electromagnetic energy can be attenuated by the use of an auto darkening lens. The description below is presented with respect to use of the invention in connection with attenuating light resulting from a welding process (sometimes referred to as “welding”), but it will be appreciated that features of the invention may be used in other environments and in connection with industrial processes other than welding, etc. Also, it will be appreciated that although a photosensor is described as the device for detecting bright light occurring during welding, other types of sensors may be used.
The intensity of light produced during welding may vary. For example, at the start of welding, the light may be very bright, but as welding continues, the light intensity may diminish. Also, the light intensity may fluctuate during sputtering, or may fluctuate in relation to the electrical energy, e.g., the AC sine wave characteristic, that may be employed in electric arc welding. Ambient light also may affect the sensor and cause welding incorrectly to be detected.
Normally the sensor or sensors for an automatic darkening lens (auto-darkening lens) and the associated circuitry are set to a given sensitivity, and any signal that is detected that exceeds a threshold level at which such sensitivity is set, whether the signal is an AC signal or a DC signal, will cause the circuitry to operate the auto-darkening lens to a dark state. A conventional approach to maintain the auto-darkening lens in dark state even after the initial striking of an arc, e.g., after which the light intensity may decrease, has been to reduce the threshold level or to increase the sensitivity of the sensor and/or associated circuit so that it continues to maintain the auto-darkening lens in the dark state even under the diminished incident light. However, such increased sensitivity or reduced threshold can cause the auto-darkening lens to remain in the dark state even when welding is not occurring, such as, for example, due to ambient light conditions. The present invention as described further below addresses this issue.
In the description herein reference will be made to a lens (also sometimes referred to as “welding lens,” “welding filter,” “shutter,” and the like), and to an automatically darkening lens (sometimes referred to as auto-darkening lens) that is able to operate automatically to control transmission of light. The lens may be a light shutter type of a device that is able to control light transmission without distorting, or at least with relatively minimal distortion, of the light and the image characteristics carried by the light or represented by the light. Therefore, when a person looks through the lens, the image seen would be substantially the same as the image seen without the lens, except that the intensity of the light transmitted through the lens may be altered depending on the operative state of the lens. The lens may be used in a welding helmet, and the lens may be used in other types of devices, such as goggles, spectacles, face masks, e.g., for industry (such as in an industrial plant or to protect outdoor or indoor electrical workers), for dentistry to protect the face of a dentist in the operative, respirator systems, nuclear flash eye protection devices, and other types of helmets, etc. Such devices usually are employed to protect the face or the eyes of a person, as is known, for example, in the field of welding and in other fields, too. Further, the lenses may be used in various other places to protect workers from bright light that could present a risk of injury.
For the purposes of providing eye protection, usually a welding lens provides light blocking characteristics in the visible, Infrared and ultraviolet wavelength ranges. The actual ranges may be determined by the components of the lens, the arrangement of those components, and so forth. One example of such a welding lens is U.S. Pat. No. 5,519,522. The lens assembly disclosed In that patent includes several liquid crystal cell light shutters, several plane polarizers, and a reflector or band pass filter, which is able to reflect ultraviolet and infrared electromagnetic energy and possibly also some electromagnetic energy in the visible wavelength range. The several liquid crystal cells, for example, may be birefringent liquid crystal cells sometimes referred to as surface mode liquid crystal cells or pi-cells.
Examples of liquid crystal cells, lenses using them and drive circuits are described in U.S. Pat. Nos. 5,208,688, 5,252,817, 5,248,880, 5,347,383, and 5,074,647. In U.S. Pat. No. 5,074,647, several different types of variable polarizer liquid crystal devices are disclosed. Twisted nematic liquid crystal cells used in an automatic shutter for welding helmets are disclosed in U.S. Pat. Nos. 4,039,254 and Re. 29,684. Exemplary birefringent liquid crystal cells useful as light shutters in the present invention are disclosed in U.S. Pat. Nos. 4,385,806, 4,436,376, 4,540,243, 4,582,396, and Re. 32,521 and exemplary twisted nematic liquid crystal cells and displays are disclosed in U.S. Pat. Nos. 3,731,986 and 3,881,809. Another type of liquid crystal light control device is known as a dyed liquid crystal cell. Such a dyed cell usually includes nematic liquid crystal material and a pleochroic dye that absorbs or transmits light according to orientation of the dye molecules. As the dye molecules tend to assume an alignment that is relative to the alignment of the liquid crystal structure or directors, a solution of liquid crystal material and dye placed between a pair of plates will absorb or transmit light depending on the alignment of the liquid crystal material. Thus, the absorptive characteristics of the liquid crystal device can be controlled as a function of applied electric field.
As is disclosed in several of the above patents, the respective shutters may have one or more operational characteristics (sometimes referred to as modes or states). One example of such an operational characteristic is the shade number; this is the darkness level or value of the shutter when it is in the light blocking mode. Another exemplary operational characteristic is the delay time during which the shutter remains in a dark state after a condition calling for the dark state, such as detection of the bright light occurring during welding, has ceased or detection thereof has terminated or been interrupted. Still another operational characteristic is sensitivity of the detection circuit and/or shutter to incident light, for example, to distinguish between ambient conditions and the bright light condition occurring during a welding operation and sensitivity also may refer to shutter response time or to the time required for the circuitry associated with the lens to detect a sharp increase in incident light (e.g., due to striking of the welding arc, etc.) and to switch the lens from the clear state to the dark state. Even another characteristic, which may be considered an operational characteristic, is the condition of the battery or other power source for the shutter, such as the amount of power remaining, operational time remaining until the power source becomes ineffective, etc. In the past various of the operational characteristics of such shutters have been adjustable or fixed.
Dynamic operational range or dynamic optical range is the operational range of the lens between the dark state and the clear state, e.g., the difference between the shade numbers of the dark state and the clear state.
The disclosures of the patents identified herein are specifically incorporated in their entirety by reference.